patch 8.1.1610: there is no way to add or load a buffer without side effects

Problem:    There is no way to add or load a buffer without side effects.
Solution:   Add the bufadd() and bufload() functions.

runtime/doc/eval.txt

@@ -2272,8 +2272,10 @@ balloon_split({msg})		List	split {msg} as used for a balloon
 browse({save}, {title}, {initdir}, {default})
 				String	put up a file requester
 browsedir({title}, {initdir})	String	put up a directory requester
+bufadd({name})			Number	add a buffer to the buffer list
 bufexists({expr})		Number	|TRUE| if buffer {expr} exists
 buflisted({expr})		Number	|TRUE| if buffer {expr} is listed
+bufload({expr})			Number	load buffer {expr} if not loaded yet
 bufloaded({expr})		Number	|TRUE| if buffer {expr} is loaded
 bufname({expr})			String	Name of the buffer {expr}
 bufnr({expr} [, {create}])	Number	Number of the buffer {expr}
@@ -3132,6 +3134,14 @@ browsedir({title}, {initdir})
 		When the "Cancel" button is hit, something went wrong, or
 		browsing is not possible, an empty string is returned.
 
+bufadd({name})						*bufadd()*
+		Add a buffer to the buffer list with {name}.
+		If a buffer for file {name} already exists, return that buffer
+		number.  Otherwise return the buffer number of the newly
+		created buffer.  When {name} is an empty string then a new
+		buffer is always created.
+		The buffer will not have' 'buflisted' set.
+
 bufexists({expr})					*bufexists()*
 		The result is a Number, which is |TRUE| if a buffer called
 		{expr} exists.
@@ -3161,6 +3171,15 @@ buflisted({expr})					*buflisted()*
 		{expr} exists and is listed (has the 'buflisted' option set).
 		The {expr} argument is used like with |bufexists()|.
 
+bufload({expr})						*bufload()*
+		Ensure the buffer {expr} is loaded.  When the buffer name
+		refers to an existing file then the file is read.  Otherwise
+		the buffer will be empty.  If the buffer was already loaded
+		then there is no change.
+		If there is an existing swap file for the file of the buffer,
+		there will be no dialog, the buffer will be loaded anyway.
+		The {expr} argument is used like with |bufexists()|.
+
 bufloaded({expr})					*bufloaded()*
 		The result is a Number, which is |TRUE| if a buffer called
 		{expr} exists and is loaded (shown in a window or hidden).

src/evalfunc.c

@@ -71,8 +71,10 @@ static void f_balloon_split(typval_T *argvars, typval_T *rettv);
 #endif
 static void f_browse(typval_T *argvars, typval_T *rettv);
 static void f_browsedir(typval_T *argvars, typval_T *rettv);
+static void f_bufadd(typval_T *argvars, typval_T *rettv);
 static void f_bufexists(typval_T *argvars, typval_T *rettv);
 static void f_buflisted(typval_T *argvars, typval_T *rettv);
+static void f_bufload(typval_T *argvars, typval_T *rettv);
 static void f_bufloaded(typval_T *argvars, typval_T *rettv);
 static void f_bufname(typval_T *argvars, typval_T *rettv);
 static void f_bufnr(typval_T *argvars, typval_T *rettv);
@@ -526,11 +528,13 @@ static struct fst
 #endif
     {"browse",		4, 4, f_browse},
     {"browsedir",	2, 2, f_browsedir},
+    {"bufadd",		1, 1, f_bufadd},
     {"bufexists",	1, 1, f_bufexists},
     {"buffer_exists",	1, 1, f_bufexists},	/* obsolete */
     {"buffer_name",	1, 1, f_bufname},	/* obsolete */
     {"buffer_number",	1, 1, f_bufnr},		/* obsolete */
     {"buflisted",	1, 1, f_buflisted},
+    {"bufload",		1, 1, f_bufload},
     {"bufloaded",	1, 1, f_bufloaded},
     {"bufname",		1, 1, f_bufname},
     {"bufnr",		1, 2, f_bufnr},
@@ -1919,6 +1923,15 @@ find_buffer(typval_T *avar)
     return buf;
 }
 
+/*
+ * "bufadd(expr)" function
+ */
+    static void
+f_bufadd(typval_T *argvars, typval_T *rettv)
+{
+    rettv->vval.v_number = buflist_add(tv_get_string(&argvars[0]), 0);
+}
+
 /*
  * "bufexists(expr)" function
  */
@@ -1940,6 +1953,25 @@ f_buflisted(typval_T *argvars, typval_T *rettv)
     rettv->vval.v_number = (buf != NULL && buf->b_p_bl);
 }
 
+/*
+ * "bufload(expr)" function
+ */
+    static void
+f_bufload(typval_T *argvars, typval_T *rettv UNUSED)
+{
+    buf_T	*buf = get_buf_arg(&argvars[0]);
+
+    if (buf != NULL && buf->b_ml.ml_mfp == NULL)
+    {
+	aco_save_T	aco;
+
+	aucmd_prepbuf(&aco, buf);
+	swap_exists_action = SEA_NONE;
+	open_buffer(FALSE, NULL, 0);
+	aucmd_restbuf(&aco);
+    }
+}
+
 /*
  * "bufloaded(expr)" function
  */

src/testdir/test_functions.vim

@@ -1515,3 +1515,31 @@ endfunc
 func Test_eventhandler()
   call assert_equal(0, eventhandler())
 endfunc
+
+func Test_bufadd_bufload()
+  call assert_equal(0, bufexists('someName'))
+  let buf = bufadd('someName')
+  call assert_notequal(0, buf)
+  call assert_equal(1, bufexists('someName'))
+  call assert_equal(0, getbufvar(buf, '&buflisted'))
+  call assert_equal(0, bufloaded(buf))
+  call bufload(buf)
+  call assert_equal(1, bufloaded(buf))
+  call assert_equal([''], getbufline(buf, 1, '$'))
+
+  let curbuf = bufnr('')
+  call writefile(['some', 'text'], 'otherName')
+  let buf = bufadd('otherName')
+  call assert_notequal(0, buf)
+  call assert_equal(1, bufexists('otherName'))
+  call assert_equal(0, getbufvar(buf, '&buflisted'))
+  call assert_equal(0, bufloaded(buf))
+  call bufload(buf)
+  call assert_equal(1, bufloaded(buf))
+  call assert_equal(['some', 'text'], getbufline(buf, 1, '$'))
+  call assert_equal(curbuf, bufnr(''))
+
+  bwipe someName
+  bwipe otherName
+  call assert_equal(0, bufexists('someName'))
+endfunc

src/version.c

@@ -777,6 +777,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1610,
 /**/
     1609,
 /**/